In an elevator, a cage is hung in an elevator-shaft by a main rope put on a traction machine and the cage is moved by driving the traction machine. The cage comprises a guiding apparatus to move along guide rails laid in a vertical direction inside the elevator-shaft. The cage is subjected to forces in directions crossing the direction of movement while moving, depending on locations where passengers are standing or baggage is placed or the weight thereof. To sustain such forces, the guiding apparatus holds the cage with a sufficient force.
Guiding apparatuses are divided into contact guiding apparatuses and noncontact magnetic guiding apparatuses. A contact guiding apparatus comprises rollers and shoes in contact with the guide rail. A magnetic guiding apparatus holds the cage in a noncontact manner by maintaining a gap to the guide rail with a magnetic force. For the contact guiding apparatus, vibration originating from irregularities on the surface of the guide rail or joints may be transmitted from rollers or shoes, or noise of roller rotation or noise of shoe abrasion may be caused. In this respect, vibration and noise are reduced for the magnetic guiding apparatus due to noncontact.
Jpn. Pat. Applin. KOKAI Publication No. 2005-350267 discloses a magnetic guiding apparatus comprising a magnet unit configured in an E shape enclosing a blade of the guide rail. The magnet unit of the guiding apparatus comprises a central electromagnet, first and second electromagnets, and first and second permanent magnets. The central electromagnet is arranged at a position opposite to the tip of the blade of the guide rail. The first and second electromagnets are arranged as a pair on both sides by nipping the blade of the guide rail therebetween. The first and second permanent magnets are connected between the first electromagnet and the central electromagnet and between the second electromagnet and the central electromagnet respectively in such a way that a magnetic flux is in line. The central electromagnet contains a third electromagnet and a fourth electromagnet. The third electromagnet is arranged in a forward portion leading to the first permanent magnet. The fourth electromagnet is arranged in a forward portion leading to the second permanent magnet.
The guiding apparatus described in Jpn. Pat. Applin. KOKAI Publication No. 2005-350267 comprises a gap sensor. The gap sensor measures the distance between the blade of the guide rail and a magnetic pole end of each of the central electromagnet and the first and second electromagnets. A cage comprises the guiding apparatus in an upper part and a lower part thereof for each of the guide rails arranged on both sides, i.e., four locations in total. The guiding apparatus individually controls the force of attraction between the guide rail and each magnetic pole based on a detection signal of the gap sensor and the value of current passed through each electromagnet. By integratively controlling the four guiding apparatuses, the elevator stabilizes the posture of the cage.
For the guiding apparatus described in Jpn. Pat. Applin. KOKAI Publication No. 2005-350267, it is necessary to increase the size of the guiding apparatus itself to generate the sufficient force of attraction with respect to the guide rail by a magnetic force. If a magnetic guiding apparatus increases in size, not only the weight thereof, but also the unit price of permanent magnets increases. Four guiding apparatuses are mounted and thus, even if each guiding apparatus grows in size only slightly, the maximum load of the cage is restricted and manufacturing costs of the elevator are raised.